title: Further studies on the hypothalamic desensitization to estrogen in immature female rats: evidence for a possible role in the control of puberty.
abstract: Immature and puberal female rats were ovariectomized and implanted with estradiol benzoate and cholesterol at the ratios of 1:120 or 1:240 into the hypothalamic ventromedial-arcuate region at 26 or 32 days of age, or on the day of the first vaginal estrus. Evaluation of the serum LH and FSH concentrations on the 2nd day after implantation revealed that the gonadotropin-inhibiting effect of the locally administered estrogen decreased between days 26 and 32 and showed a further distinct decline at the time of puberty. In a second experiment, uterine weight and serum LH and FSH levels were monitored in untreated immature female rats at daily intervals from 25 to 36 days of age. Relatively high values for both gonadotropins were recorded between days 25 and 28. Accelerated uterine growth around day 30 indicating increasing estrogen secretion was associated with a sudden decrease of LH and FSH concentration in the blood. After that, LH and, to a less degree FSH levels began to rise in spite of further weight gain of the uterus. The results suggest that the hypothalamic sensitivity to the gonadotropin-inhibiting effect of estrogen declines during the last week before the onset of puberty. Together with other findings they furthermore indicate that this desensitization process may be involved in the neurohormonal control of puberty in female rats.
mesh_terms: D000818:Animals; D004967:Estrogens / Q000502:physiology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000032:analysis; D006062:Gonadotropins / Q000037:antagonists & inhibitors; D007986:Luteinizing Hormone / Q000032:analysis; D009929:Organ Size; D010053:Ovary / Q000502:physiology; D051381:Rats; D012741:Sexual Maturation; D014599:Uterus / Q000502:physiology
chemical_list: D004967:Estrogens; D006062:Gonadotropins; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone